1. Technical Field
This invention is related to an apparatus for optical interferometric measurement (optical interferometric measurement apparatus) and a method for the same. In particular, this invention is related to the apparatus and the method adapted to measure a movement of an object in shorter than or equal to the nanometer scale by acquiring a shift of a phase of an interference signal. The shift can be measured by using a point-spread-function that is determined by applying Fourier transform to the interference signal.
Conventionally, an optical interferometric measurement apparatus has been known. The conventional apparatus is configured to acquire measurement data by periodically sampling a spectrum interference signal, which is detected by an interferometer, and to determine a point-spread-function by applying Fourier transform to the acquired measurement data, thereby measuring a movement of an object based on a shift amount of a peak position in the determined point-spread-function.
This conventional optical interferometric measurement apparatus is, however, not able to detect (measure) a movement of the object in shorter than or equal to a micrometer scale since the point-spread-function itself spreads in the micrometer scale (i.e., the resolution of the point-spread-function is micrometer scale).
2. Description of Related Art
Here, an optical interferometric measurement apparatus that can measure a movement of an object in the sub-nanometer scale is taught by Non Patent Literature 1 (NPL 1): B. Braaf et al., “Phase-stabilized optical frequency domain imaging at 1-μm for the measurement of blood flow in the human choroid,” Optics Express, USA, October 2011, Vol 19, No. 22, pp. 20886-20903. The apparatus of NPL1 is equipped with an optical interferometer for measurement (measuring interferometer) and an optical interferometer for reference (referring interferometer), acquires monitoring data by sampling a spectrum interference signal detected by the referring interferometer and measurement data by sampling a spectrum interference signal detected by the measuring interferometer, calculates correlation between the acquired monitoring data and the acquired measurement data, and removes a noise of the spectrum interference signal detected by the measuring interferometer, thereby achieving a measurement in the sub-nanometer scale.